A non-linear theoretical dry/wet boundary-based two-source trapezoid model for estimation of land surface evapotranspiration

ABSTRACT It is well known that the dry/wet boundaries of land surface temperature fractional vegetation coverage (LSTfc) trapezoid framework vary linearly with vegetation coverage (fc). In this study, the theoretical end-members algorithm is modified to continuously estimate the dry/wet end-members under varying vegetation conditions, causing the theoretical dry/wet boundaries to become non-linear. The findings revealed that the non-linear dry/wet boundaries were generally below the conventional linear dry/wet boundaries. Furthermore, the non-linear boundary scheme adopted herein provided better performance in estimating the latent heat flux (LE) and vegetation latent heat flux fraction (LEv/LE) compared to the linear boundary scheme. The parametric schemes of aerodynamic and thermodynamic roughness length and the aerodynamic resistance were the major drivers that result in dry/wet boundaries characteristics being highly non-linear. This study enhanced the physical process description in the LST-fc trapezoid framework and improved the prediction accuracy of regional LE and its components.